Dataset Information

Dioxomolybdenum(VI) complexes with ene-1,2-dithiolate ligands: synthesis, spectroscopy, and oxygen atom transfer reactivity.

ABSTRACT: New dioxomolybdenum(VI) complexes, (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdt)] (2) and (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdtCl(2))](4)(S(2)C(2)(CO(2)Me)(2) = 1,2-dicarbomethoxyethylene-1,2-ditholate, bdt = 1,2-benzenedithiolate, bdtCl(2) = 3,6-dichloro-1,2-benzenedithiolate), that possess at least one ene-1,2-dithiolate ligand were synthesized by the reaction of their mono-oxo-molybdenum(IV) derivatives, (Et(4)N)(2)[Mo(IV)O(S(2)C(2)(CO(2)Me)(2))(bdt)] (1) and (Et(4)N)(2)[Mo(IV)O(S(2)C(2)(CO(2)Me)(2))(bdtCl(2))] (3), with Me(3)NO. Additionally, the bis(ene-1,2-dithiolate)Mo(VI)O(2) complex, (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(2)] (6), was isolated. Complexes 2, 4, and 6 were characterized by elemental analysis, negative-ion ESI mass spectrometry, and IR spectroscopy. X-ray analysis of 4 and 6 revealed a Mo(VI) center that adopts a distorted octahedral geometry. Variable-temperature (1)H NMR spectra of (CD(3))(2)CO solutions of the Mo(VI)O(2) complexes indicated that the Mo centers isomerize between Delta and Lambda forms. The electronic structures of 2, 4, and 6 have been investigated by electronic absorption and resonance Raman spectroscopy and bonding calculations. The results indicate very similar electronic structures for the complexes and considerable pi-delocalization between the Mo(VI)O(2) and ene-1,2-dithiolate units. The similar oxygen atom transfer kinetics for the complexes results from their similar electronic structures.

SUBMITTER: Sugimoto H

PROVIDER: S-EPMC4872601 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Dioxomolybdenum(VI) complexes with ene-1,2-dithiolate ligands: synthesis, spectroscopy, and oxygen atom transfer reactivity.

Sugimoto Hideki H Tatemoto Susumu S Suyama Koichiro K Miyake Hiroyuki H Itoh Shinobu S Dong Chao C Yang Jing J Kirk Martin L ML

Inorganic chemistry 20091101 22

New dioxomolybdenum(VI) complexes, (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdt)] (2) and (Et(4)N)(Ph(4)P)[Mo(VI)O(2)(S(2)C(2)(CO(2)Me)(2))(bdtCl(2))](4)(S(2)C(2)(CO(2)Me)(2) = 1,2-dicarbomethoxyethylene-1,2-ditholate, bdt = 1,2-benzenedithiolate, bdtCl(2) = 3,6-dichloro-1,2-benzenedithiolate), that possess at least one ene-1,2-dithiolate ligand were synthesized by the reaction of their mono-oxo-molybdenum(IV) derivatives, (Et(4)N)(2)[Mo(IV)O(S(2)C(2)(CO(2)Me)(2))(bdt)] (1) and (Et(4)N) ...[more]

PMID: 19831360

Similar Datasets

Project description:New square-pyramidal bis(ene-1,2-dithiolate)MoSe complexes, [Mo(IV)Se(L)(2)](2-), have been synthesised along with their terminal sulfido analogues, [Mo(IV)S(L)(2)](2-), using alkyl (L(C(4)H(8))), phenyl (L(Ph)) and methyl carboxylate (L(COOMe)) substituted dithiolene ligands (L). These complexes now complete three sets of Mo(IV)O, Mo(IV)S and Mo(IV)Se species that are coordinated with identical ene-1,2-dithiolate ligands. The [alkyl substituted Mo(S/Se)(L(C(4)H(8)))(2)](2-) complexes were reported in prior investigations (H. Sugimoto, T. Sakurai, H. Miyake, K. Tanaka and H. Tsukube, Inorg. Chem. 2005, 44, 6927, H. Tano, R. Tajima, H. Miyake, S. Itoh and H. Sugimoto, Inorg. Chem. 2008, 47, 7465). The new series of complexes enable a systematic investigation of terminal chalcogenido and supporting ene-1,2-dithiolate ligand effects on geometric structure, electronic structure, and spectroscopic properties. X-ray crystallographic analysis of these (Et(4)N)(2)[MoEL(2)] (E = terminal chalocogenide) complexes reveals an isostructural Mo centre that adopts a distorted square pyramidal geometry. The M≡E bond distances observed in the crystal structures and the ν(M≡E) vibrational frequencies indicate that these bonds are weakened with an increase in L→Mo electron donation (L(COOMe) < L(Ph) < L(C(4)H(8))), and this order is confirmed by an electrochemical study of the complexes. The (77)Se NMR resonances in MoSeL complexes appear at lower magnetic fields as the selenido ion became less basic from MoSeL(C(4)H(8)), MoSeL(Ph) and MoSeL(COOMe). Electronic absorption and resonance Raman spectroscopies have been used to assign key ligand-field, MLCT, LMCT and intraligand CT bands in complexes that possess the L(COOMe) ligand. The presence of low-energy intraligand CT transition in these MoEL(COOMe) compounds directly probes the electron withdrawing nature of the -COOMe substituents, and this underscores the complex electronic structure of square pyramidal bis(ene-1,2-dithiolate)-Mo(IV) complexes that possess extended dithiolene conjugation.

Project description:Oxoiron(IV) species have been found to act as the oxidants in the catalytic cycles of several mononuclear nonheme iron enzymes that activate dioxygen. To gain insight into the factors that govern the oxidative reactivity of such complexes, a series of five synthetic S = 1 [Fe(IV)(O)(L(N5))](2+) complexes has been characterized with respect to their spectroscopic and electrochemical properties as well as their relative abilities to carry out oxo transfer and hydrogen atom abstraction. The Fe=O units in these five complexes are supported by neutral pentadentate ligands having a combination of pyridine and tertiary amine donors but with different ligand frameworks. Characterization of the five complexes by X-ray absorption spectroscopy reveals Fe=O bonds of ca. 1.65 Å in length that give rise to the intense 1s?3d pre-edge features indicative of iron centers with substantial deviation from centrosymmetry. Resonance Raman studies show that the five complexes exhibit ?(Fe=O) modes at 825-841 cm(-1). Spectropotentiometric experiments in acetonitrile with 0.1 M water reveal that the supporting pentadentate ligands modulate the E(1/2)(IV/III) redox potentials with values ranging from 0.83 to 1.23 V vs. Fc, providing the first electrochemical determination of the E(1/2)(IV/III) redox potentials for a series of oxoiron(IV) complexes. The 0.4-V difference in potential may arise from differences in the relative number of pyridine and tertiary amine donors on the L(N5) ligand and in the orientations of the pyridine donors relative to the Fe=O bond that are enforced by the ligand architecture. The rates of oxo-atom transfer (OAT) to thioanisole correlate linearly with the increase in the redox potentials, reflecting the relative electrophilicities of the oxoiron(IV) units. However this linear relationship does not extend to the rates of hydrogen-atom transfer (HAT) from 1,3-cyclohexadiene (CHD), 9,10-dihydroanthracene (DHA), and benzyl alcohol, suggesting that the HAT reactions are not governed by thermodynamics alone. This study represents the first investigation to compare the electrochemical and oxidative properties of a series of S = 1 Fe(IV)=O complexes with different ligand frameworks and sheds some light on the complexities of the reactivity of the oxoiron(IV) unit.

Project description:We report the syntheses, crystal structures, and characterization of the novel cis-dioxomolybdenum(VI) complexes [Tpm*MoVIO2Cl](MoO2Cl3) (1) and [Tpm*MoVIO2Cl](ClO4) (2), which are supported by the charge-neutral tris(3,5-dimethyl-1-pyrazolyl)methane (Tpm*) ligand. A comparison between isostructural [Tpm*MoVIO2Cl]+ and Tp*MoVIO2Cl [Tp* = hydrotris(3,5-dimethyl-1-pyrazolyl)borate] reveals the effects of one unit of overall charge difference on their spectroscopic and electrochemical properties, geometric and electronic structures, and O-atom-transfer (OAT) reactivities, providing new insight into pyranopterin molybdoenzyme OAT reactivity. Computational studies of these molecules indicate that the delocalized positive charge lowers the lowest unoccupied molecular orbital (LUMO) energy of cationic [Tpm*MoO2Cl]+ relative to Tp*MoO2Cl. Despite their virtually identical geometric structures revealed by crystal structures, the MoVI/MoV redox potential of 2 is increased by 350 mV relative to that of Tp*MoVIO2Cl. This LUMO stabilization also contributes to an increased effective electrophilicity of [Tpm*MoO2Cl]+ relative to that of Tp*MoO2Cl, resulting in a more favorable resonant interaction between the molydenum complex LUMO and the highest occupied molecular orbital (HOMO) of the PPh3 substrate. This leads to a greater thermodynamic driving force, an earlier transition state, and a lowered activation barrier for the orbitally controlled first step of the OAT reaction in the Tpm* system relative to the Tp* system. An Eyring plot analysis shows that this initial step yields an O≡MoIV-OPPh3 intermediate via an associative transition state, and the reaction is ∼500-fold faster for 2 than for Tp*MoO2Cl. The second step of the OAT reaction entails solvolysis of the O≡MoIV-OPPh3 intermediate to afford the solvent-substituted MoIV product and is 750-fold faster for the Tpm* system at -15 °C compared to the Tp* system. The observed rate enhancement for the second step is ascribed to a switch of the reaction mechanism from a dissociative pathway for the Tp* system to an alternative associative pathway for the Tpm* system. This is due to a more Lewis acidic MoIV center in the Tpm* system.

Project description:The oxygen atom transfer reactivity of the dioxo-Mo(VI) complex, Tp(iPr)MoO(2)(OPh) (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate), with a range of tertiary phosphines (PMe(3), PMe(2)Ph, PEt(3), PBu(n)(3), PEt(2)Ph, PEtPh(2), and PMePh(2)) has been investigated. The first step in all the reactions follows a second-order rate law indicative of an associative transition state, consistent with nucleophilic attack by the phosphine on an oxo ligand, namely, Tp(iPr)MoO(2)(OPh) + PR(3) --> Tp(iPr)MoO(OPh)(OPR(3)). The calculated free energy of activation for the formation of the OPMe(3) intermediate (Chem. Eur. J. 2006, 12, 7501) is in excellent agreement with the experimental DeltaG() value reported here. The second step of the reaction, that is, the exchange of the coordinated phosphine oxide by acetonitrile, Tp(iPr)MoO(OPh)(OPR(3)) + MeCN --> Tp(iPr)MoO(OPh)(MeCN) + OPR(3), is first-order in starting complex in acetonitrile. The reaction occurs via a dissociative interchange (I(d)) or associative interchange (I(a)) mechanism, depending on the nature of the phosphine oxide. The activation parameters for the solvolysis of Tp(iPr)MoO(OPh)(OPMe(3)) (DeltaH(++) = 56.3 kJ mol(-1); DeltaS(++) = -125.9 J mol(-1) K(-1); DeltaG(++) = 93.8 kJ mol(-1)) and Tp(iPr)MoO(OPh)(OPEtPh(2)) (DeltaH(++) = 66.5 kJ mol(-1); DeltaS(++) = -67.6 J mol(-1) K(-1); DeltaG(++) = 86.7 kJ mol(-1)) by acetonitrile are indicative of I(a) mechanisms. In contrast, the corresponding parameters for the solvolysis reaction of Tp(iPr)MoO(OPh)(OPEt(3)) (DeltaH(++) = 95.8 kJ mol(-1); DeltaS(++) = 26.0 J mol(-1) K(-1); DeltaG(++) = 88.1 kJ mol(-1)) and the remaining complexes by the same solvent are indicative of an I(d) mechanism. The equilibrium constant for the solvolysis of the oxo-Mo(V) phosphoryl complex, [Tp(iPr)MoO(OPh)(OPMe(3))](+), by acetonitrile was calculated to be 1.9 x 10(-6). The oxo-Mo(V) phosphoryl complex is more stable than the acetonitrile analogue, whereas the oxo-Mo(IV) acetonitrile complex is more stable than the phosphoryl analogue. The higher stability of the Mo(V) phosphoryl complex may explain the phosphate inhibition of sulfite oxidase.

Dataset Information

Dioxomolybdenum(VI) complexes with ene-1,2-dithiolate ligands: synthesis, spectroscopy, and oxygen atom transfer reactivity.

Publications

Dioxomolybdenum(VI) complexes with ene-1,2-dithiolate ligands: synthesis, spectroscopy, and oxygen atom transfer reactivity.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets